1. Field of the Invention
The present general inventive concept generally relates to an image forming apparatus and a method of controlling a motor, and more particularly, to an image forming apparatus to control a velocity variation between photosensitive media and to minimize a color dislocation by controlling a phase and a velocity of the other motors based on one motor from among a plurality of motors, and a method of controlling a motor.
2. Description of the Related Art
In general, an image forming apparatus may use an electronography as a laser printer, a copy machine, a multifunctional device, and a facsimile and may include an optical scanner. The image forming apparatus forms an electrostatic latent image on a surface of a photosensitive medium by using an optical beam which is outputted from the optical scanner, transfers the electrostatic latent image on a paper, and prints out a desired image.
Meanwhile, an electronography-type printer like a color laser printer includes four photosensitive media which are provided to correspond to four colors of yellow, cyan, magenta, and black, an exposure unit which forms an electrostatic latent image of a desired image by directing a light at each of the photosensitive media, a developer which develops the electrostatic latent image with a developing agent for each color, and an image forming medium (or a transfer belt or an intermediate transfer belt) which receives images developed in the respective photosensitive media to be sequentially overlapped with each other, forms an image with a completed color, and transfers the image on a paper.
Accordingly, in order to print out a desired color image, the image is developed with each color in four photosensitive media, imprinted to be overlapped on a same image position on an image forming medium so as to be a final color image, and printed out on a paper.
Meanwhile, in order to obtain a color image which is exactly matched with a desired color by overlapping the four colors on the same image position on the image forming medium, a start point and an end point where the image is transferred from the photosensitive media to the image forming medium should be exactly consistent with each other in all cases of the four colors. That is, even though images are developed clearly in the four photosensitive media, a finally obtained color image fails to express the desired colors and image if the images are transferred in the image forming medium to be slightly dislocated.
Accordingly, in order to express a desired color image, it is important to match a point of time of starting an exposure of each of the photosensitive media by the exposure unit by considering a driving velocity of the image forming medium. As such, an operation of adjusting a point of time of starting the exposure so that a plurality of colors for forming an image are precisely overlapped with each other is referred to as a color registration.
However, a photosensitive medium has a periodic velocity variation. Such periodic velocity variation occurs in all rotator systems unless it is an ideally impeccable rotator system, which may be resulted from a shape error of a photosensitive medium (eccentricity, run-out, etc.), a characteristic of a medium related to alignment or installation, a gear shape error, a gear transmission error, a structural incompleteness of a gear train, a coupling angle transmission error, etc. The velocity variation of the photosensitive media causes a color dislocation.
In this regard, efforts for controlling a structural stability of a driving unit and a developer, a degree in applying a gear, a degree of coupling, and a tolerance have been made in order to reduce the color dislocation.
However, even though the structural incompleteness is resolved to a certain degree, there still has been a limit to obtain an impeccable constant velocity of a photosensitive medium, and thus, a method of calculating a dislocation variation for each photosensitive medium and controlling a motor velocity according to the calculated dislocation variation may be additionally used.
Therefore, such a conventional method incurs high costs since it requires an independent control for each photosensitive medium, and a problem where other source to be driven than a developing unit which is not sensitive to a velocity variation are out of control since each motor has a velocity variation.